Clinicopathologic Analysis of the Micropapillary Variant of Urothelial Carcinoma in Urinary

ABSTRACT

BACKGROUND: Micropapillary urothelial carcinoma of urinary bladder is a rare and aggressive subtype of urothelial carcinoma (UC). METHODS AND RESULTS: Seven UCs with a micropapillary component (MPC) were identified by reviewing 135 cystectomy specimens of UC (5.2% in incidence). MPC was associated with conventional UC in 6 cases and the plasmacytoid variant of UC in 1 case. Lymph node metastasis, that characteristically contained MPC was present in 60% (3 out of 5 cases of regional lymph node dissection). Three patients with extensive MPC showed laminar propria invasion (pT1; 33%) and perivesical fat invasion (pT3; 67%). Two out of 3 patients with extensive MPC showed distant metastasis into the colon after cystectomy. The colonic lesions showed exclusively micropapillary differentiation. Four patients with focal or moderate MPC (pT2, 25%; pT3, 75%) were alive without disease at the time of writing this article. All 3 cases with extensive MPC had surface and/or invasive MPC on the prior TURB specimen. Immunohistochemically, the tumor cells were positive for cytokeratin 7, cytokeratin 20, EMA and E-cadherin and tissue retraction spaces that simulate lymphatic spaces were negative for CD34 in all 7 cases. CONCLUSIONS: This study suggests that the micropapillary growth pattern in UC is a manifestation of aggressive behavior and UC with MPC must be included as part of the differential diagnosis when dealing with a metastatic lesion with a micropaillary structure.